This invention relates generally to lighting controls, and more particularly to direct current low voltage pulse width modulated incandescent lamp controllers having two terminals suitable for connection in series with an electrical power source and load.
Techniques for lamp intensity control include several methods and apparatus with which problems and solutions for direct current low voltage pulse width modulated insulated gate dimmers are discussed and disclosed. In U.S. Pat. No. 5,113,120 (Scott, et al.) the timing wave form supply is increased in voltage by a charge pump voltage doubler, thus allowing n-channel field effect transistors to be used in series with the power supply and load. This approach works well for voltages in the 10 to 30 volt range, and at pulse repetition rates of approximately 70 Hz. In U.S. Pat. No. 5,519,287 (Goodale et al.), to which this application is related, the timing wave form is differentiated by a capacitor and stepped up in voltage by an auto transformer, then applied to the gate of the Mosfet. This circuit enables placement of the entire dimmer in series with the power supply and load, allowing operation down to about 3.5 volts, but also has a low pulse repetition rate. With both of these methods the timing wave form produced is not much more than twice that of the supply voltage. And the manner in which the timing circuitry controls the FET results in transitions from On to Off and vice versa of the field effect semiconductor being limited in rapidity, thus requiring a reduced pulse rate as to secure enhanced efficiency. Furthermore, neither of the above methods provide load or power source regulation.
This invention has as one object a means to simply yet effectively increase the timing voltage to many times that of the supply voltage as to afford maximized efficiency by the field effect transistor.
A related object is to allow the option of a relatively high pulse repetition frequency with the attendant advantages of smaller component values, and versatility/flexibility in use with bulbs having small filaments with reduced thermal inertia.
A further related object of this invention is to provide full operation of lamp intensity control down to a supply voltage of 2 volts or less, and with a simple start circuit, down to 1 volt or less. But, with or without the start circuit, the controller is compatible with higher voltage applications of 18 volts or more.
Still another object is to afford a lamp controller having two terminals with input voltage responsive lamp intensity regulation wherein the lamp may be fully dimmed by operator manual control, yet maintain the same brightness over a considerable range of supply voltage.
And again another object is to provide two terminal illumination output responsive lamp intensity regulation with the benefits as just mentioned in the previous object, while retaining the advantages attendant to increased timing voltage.